LTT DID NOT BEGIN DESCENT IN TIME TO MEET ALT CROSSING RESTRICTION.

Narrative

WE WERE ON THE LAST LEG HOME OF AN EXHAUSTING 4 DAY TRIP. BOTH OF US WERE VERY TIRED ESPECIALLY AFTER A PERIOD OF REDUCED 'REST'. WHILE I WAS CALLING IN RANGE TO OUR COMPANY THE CAPT WAS ISSUED A CLRNC FOR A PD DSCNT TO CROSS 40 DME SE OF ATL AT 8000'. UNFORTUNATELY; A SMALL UNRULY CHILD SEATED DIRECTLY BEHIND THE COCKPIT BEGAN TO CAUSE TROUBLE IN AN APPARENT EFFORT TO GAIN ATTN FROM HIS MOTHER. THE CHILD KICKED THE WALLS; MADE LOUD NOISES; AND EVEN TRIED TO GET INTO THE CAPT'S FLT BAG. (THE COCKPIT DOOR ON THE LTT IS NEVER CLOSED DURING THE SUMMER MONTHS DUE TO EXTREMELY POOR COCKPIT VENTILATION.) THE CHILD CONTINUED THIS TYPE OF BEHAVIOR FOR SOME TIME BEFORE FINALLY CALMING DOWN. THE CAPT THEN ASKED THAT I TAKE CONTROL OF THE ACFT SO THAT HE COULD FILL OUT HIS PERSONAL LOGBOOK. ABOUT 40 SECONDS AFTER TAKING CONTROL OF THE ACFT ATC QUERIED US AS TO OUR ALT. WE WERE 40 DME AT 11000. WE BOTH IMMEDIATELY REALIZED THAT THE UNRULY CHILD HAD DISTRACTED US FROM THE DSCNT CLRNC. THE CAPT TOOK CONTROL OF THE ACFT (WITHOUT VERBAL ACKNOWLEDGEMENT); AND STARTED AN ABRUPT AND STEEP DSCNT. THE CAPT LEVELED AT 8000' BY 38.3 DME. I CLOSED THE COCKPIT DOOR. WE BOTH BURNED UP FOR THE REST OF THE FLT. (THERE IS NO COCKPIT AIR CONDITIONING; LET ALONE AIR MOVEMENT IN OLDER LTT'S.) ONE LAST COMMENT. I DO BELIEVE A F/A WOULD'VE BEEN HELPFUL IN THIS SITUATION. TOO BAD THAT F/A'S ARE NOT REQUIRED ON ACFT WITH 19 SEATS OR LESS!